BUG (string dtype): convert dictionary input to materialized string array in ArrowStringArray constructor (#59479)

Author: jorisvandenbossche

pandas/core/arrays/string_arrow.py

@@ -130,18 +130,22 @@ class ArrowStringArray(ObjectStringArrayMixin, ArrowExtensionArray, BaseStringAr
 
     def __init__(self, values) -> None:
         _chk_pyarrow_available()
-        if isinstance(values, (pa.Array, pa.ChunkedArray)) and pa.types.is_string(
-            values.type
+        if isinstance(values, (pa.Array, pa.ChunkedArray)) and (
+            pa.types.is_string(values.type)
+            or (
+                pa.types.is_dictionary(values.type)
+                and (
+                    pa.types.is_string(values.type.value_type)
+                    or pa.types.is_large_string(values.type.value_type)
+                )
+            )
         ):
             values = pc.cast(values, pa.large_string())
 
         super().__init__(values)
         self._dtype = StringDtype(storage=self._storage, na_value=self._na_value)
 
-        if not pa.types.is_large_string(self._pa_array.type) and not (
-            pa.types.is_dictionary(self._pa_array.type)
-            and pa.types.is_large_string(self._pa_array.type.value_type)
-        ):
+        if not pa.types.is_large_string(self._pa_array.type):
             raise ValueError(
                 "ArrowStringArray requires a PyArrow (chunked) array of "
                 "large_string type"

pandas/tests/arrays/string_/test_string_arrow.py

@@ -88,19 +88,18 @@ def test_constructor_not_string_type_value_dictionary_raises(chunked):
         ArrowStringArray(arr)
 
 
-@pytest.mark.xfail(
-    reason="dict conversion does not seem to be implemented for large string in arrow"
-)
+@pytest.mark.parametrize("string_type", ["string", "large_string"])
 @pytest.mark.parametrize("chunked", [True, False])
-def test_constructor_valid_string_type_value_dictionary(chunked):
+def test_constructor_valid_string_type_value_dictionary(string_type, chunked):
     pa = pytest.importorskip("pyarrow")
 
-    arr = pa.array(["1", "2", "3"], pa.large_string()).dictionary_encode()
+    arr = pa.array(["1", "2", "3"], getattr(pa, string_type)()).dictionary_encode()
     if chunked:
         arr = pa.chunked_array(arr)
 
     arr = ArrowStringArray(arr)
-    assert pa.types.is_string(arr._pa_array.type.value_type)
+    # dictionary type get converted to dense large string array
+    assert pa.types.is_large_string(arr._pa_array.type)
 
 
 def test_constructor_from_list():